Method of fabricating a semiconductor device structure

1. A method for fabricating a semiconductor device structure, comprising:

forming a fin structure over a substrate;

forming a gate structure over the fin structure;

epitaxially growing a source/drain structure covering the fin structure, wherein the source/drain structure has a (100) surface and a (111) surface;

epitaxially growing a capping layer over the source/drain structure, wherein the capping layer has a top portion epitaxially grown from the (100) surface of the source/drain structure and a lower portion under the top portion and epitaxially grown from the (111) surface of the source/drain structure, the top portion has a first thickness and the lower portion has a second thickness, and a ratio of the first thickness to the second thickness is in a range of about 1.01 to about 2;

etching the top portion and the lower portion of the capping layer to expose the source/drain structure;

forming a silicide layer over the source/drain structure; and

forming a contact over the silicide layer.

2. The method as claimed in claim 1 , wherein epitaxially growing the source/drain structure comprises:

introducing a Ge-containing precursor so that the source/drain structure has a first atomic percentage of Ge; and

introducing a B-containing precursor so that the source/drain structure has a first dopant concentration of B, and wherein epitaxially growing the capping layer comprises:

introducing a Ge-containing precursor so that the capping layer has a second atomic percentage of Ge which is smaller than the first atomic percentage; and

introducing a B-containing precursor so that the capping layer has a second dopant concentration of B which is lower than the first dopant concentration.

3. The method as claimed in claim 2 , wherein the second atomic percentage of Ge is in a range of about 1% to about 35%.

4. The method as claimed in claim 2 , wherein the second dopant concentration of B is in a range of about 1×10 19 /cm 3 to about 8×10 20 /cm 3 .

5. The method as claimed in claim 2 , wherein epitaxially growing the capping layer further comprises:

introducing HCl gas, wherein a flow rate of the HCl gas is in a range of about 10 sccm to about 1000 sccm.

6. The method as claimed in claim 1 , wherein the silicide layer has a surface which is substantially level with a surface of the lower portion of the capping layer.

7. The method as claimed in claim 1 , wherein etching the capping layer comprises performing a dry etching process, and performing the dry etching process comprises:

introducing a reactant gas, wherein the reactant gas comprises Cl 2 , CF 4 , C 4 F 6 or CH 3 F.

8. A method for fabricating a semiconductor device structure, comprising:

forming a fin structure over a substrate;

forming a gate structure over the fin structure;

epitaxially growing a first portion of a source/drain structure over the fin structure, wherein the first portion of the source/drain structure has a first atomic percentage of Ge;

epitaxially growing a capping layer covering the first portion of the source/drain structure, wherein the capping layer has a second atomic percentage of Ge that is smaller than the first atomic percentage of Ge;

etching the capping layer to expose the source/drain structure;

forming a silicide layer over the source/drain structure; and

forming a contact over the silicide layer.

9. The method as claimed in claim 8 , further comprising:

epitaxially growing a second portion of a source/drain structure between the first portion of the source/drain structure and the fin structure, wherein the second portion of the source/drain structure has a third atomic percentage of Ge that is smaller than the first atomic percentage of Ge.

10. The method as claimed in claim 9 , wherein the first atomic percentage of Ge is in a range of about 20% to about 80%, the second atomic percentage of Ge is in a range of about 1% to about 35%, and the third atomic percentage of Ge is in a range of about 10% to about 40%.

11. The method as claimed in claim 9 , wherein epitaxially growing the second portion of the source/drain structure comprises:

forming fin spacers over sidewalls of the fin structure;

recessing the fin structure to form a recess between the fin spacers and over the fin structure; and

epitaxially growing the second portion of the source/drain structure in the recess.

12. The method as claimed in claim 8 , wherein epitaxially growing the capping layer comprises:

introducing a B-containing precursor so that the capping layer has a dopant concentration of B which is in a range of about 1×10 19 /cm 3 to about 8×10 20 /cm 3 .

13. The method as claimed in claim 8 , wherein epitaxially growing the capping layer comprises:

introducing HCl gas, wherein the flow rate of the HCl gas is in a range of about 10 sccm to about 1000 sccm.

14. The method as claimed in claim 8 , wherein epitaxially growing the capping layer comprises:

epitaxially growing a top portion of the capping layer from a (100) surface of the source/drain structure and epitaxially growing a lower portion of the capping layer under the top portion of the capping layer from a (111) surface of the source/drain structure

wherein etching the capping layer comprises:

etching the top portion and the lower portion of the capping layer, wherein the top portion is removed completely, and the first portion of the source/drain structure is exposed by the lower portion of the capping layer, and wherein a ratio of a thickness of the top portion to a thickness of the lower portion is in a range of about 1.01 to about 2 before etching the capping layer.

15. The method as claimed in claim 8 , wherein an angle between the silicide layer and the capping layer is in a range of about 30° to about 75°.

16. A method for fabricating a semiconductor device structure, comprising:

forming a fin structure over a substrate;

forming a gate structure over the fin structure;

epitaxially growing a source/drain structure over the fin structure;

epitaxially growing a top portion of a capping layer from a (100) surface of the source/drain structure and epitaxially growing a lower portion of the capping layer that is under the top portion of the capping layer from a (111) surface of the source/drain structure, wherein the top portion has a first thickness and the lower portion has a second thickness, and the first thickness is larger than the second thickness, and wherein epitaxially growing the capping layer comprises:

introducing a Ge-containing precursor so that the capping layer has an atomic percentage of Ge which is in a range of about 1% to about 35%; and

introducing HCl gas;

etching the top portion and the lower portion under the top portion of the capping layer to expose the source/drain structure;

forming a silicide layer over the source/drain structure; and

forming a contact over the silicide layer.

17. The method as claimed in claim 16 , wherein a ratio of the first thickness of the top portion to the second thickness of the lower portion is in a range of about 1.01 to about 2 before etching the capping layer.

18. The method as claimed in claim 17 , wherein the first thickness is in a range of about 1 nm to about 10 nm, and the second thickness is in a range of about 0.5 nm to about 9.5 nm.

19. The method as claimed in claim 16 , wherein epitaxially growing the capping layer comprises:

introducing a B-containing precursor so that the capping layer has a dopant concentration of B which is in a range of about 1×10 19 /cm 3 to 8×10 20 /cm 3 .

20. The method as claimed in claim 16 , wherein the flow rate of the HCl gas is in a range of about 10 sccm about 1000 sccm.